A nanoimprinting (NIL) method is a technique obtained by developing an embossing technique which is well-known in the production of optical disks, in which a mold on which a concave-convex pattern is formed is pressed to a resist to be dynamically deformed, thereby precisely transferring a fine pattern. Among the techniques, an optical nanoimprinting method is a technique of applying light through a transparent mold or a transparent base material, photo-curing a photocurable composition, thereby performing transfer. Since it is possible to perform imprinting at room temperature, improvement of dimensional stability and improvement of a throughput are expected. When a mold is produced once, since a nanostructure having a size of ten to several hundreds of nanometers can be easily and repeatedly molded, it is economical. Further, since the technique is a nano processing technique with less hazardous waste and discharge, recently, the application of this technique to various fields has been expected.
As characteristics required for a resist used for optical nanoimprinting, etching resistance, releasing properties, filling properties in a mold, and coating properties on a substrate are exemplified. When a resist is applied to an LED, since the resist is used as a mask for forming a moth-eye structure on a substrate of the LED, pattern forming properties and dry etching resistance are required. In the hard disk drive (HDD) field, application to production of patterned media in which ten to several tens of nanometers of a periodic pattern is imprinted in the entire media is expected and filling properties (low viscosity) are required in addition to pattern forming properties and dry etching resistance. In the semiconductor field, as a method of forming a device pattern having a size of ten to several tens of nanometers, a nanoimprinting method is exemplified along with extreme ultraviolet exposure (EUV). Even in the present application, filling properties (low viscosity) and a solventless condition are required in addition to pattern forming properties and dry etching resistance.
As a polymerizable compound for imprinting, a compound having a fluorene skeleton has been known. For example, PTL 1 discloses an imprint material which includes a compound having a bisaryl fluorene skeleton, a compound having at least one polymerizable group in a molecule, and a photopolymerization initiator. Though, in PTL 1, neopentyl glycol diacrylate is exemplified as the compound having at least one polymerizable group in a molecule, the compound is not preferable from the viewpoint of degraded dry etching resistance. Moreover, since the compound having a bisaryl fluorene skeleton is contained in the range of 50 parts by mass to 95 parts by mass, the composition becomes highly viscous and pattern formation is degraded. Further, dry etching resistance is not mentioned in this literature.
Further, PTL 2 discloses a photocurable composition which contains difunctional (meth)acrylate having a fluorene skeleton. However, in this literature, the (meth)acrylate having a fluorene skeleton is used for providing curing properties, scratch resistance, rigidity, and transparency and dry etching resistance is not mentioned.
PTL 3 discloses an imprint material which includes a compound having five or more polymerizable groups in a molecule, a compound having two polymerizable groups in a molecule, and a photo-radical generator and forms a high hardness film. However, even in PTL 3, a compound with degraded dry etching resistance is used. Furthermore, dry etching resistance is not mentioned in this literature.
PTL 4 discloses a photocurable composition for optical nanoimprint lithography which includes a polymerizable compound having a primary skin irritation (PII value) of 4.0 or less and whose viscosity at 25° C. is in the range of 3 mPa·s to 18 mPa·s, but a compound with degraded dry etching resistance is used even in this literature. Moreover, etching resistance in this literature is not dry etching but wet etching.
PTL 5 discloses a photo-curable nanoimprint resist material which includes a composition containing a (meth)acrylate monomer having a cyclic structure and/or an oligomer thereof and a photopolymerization initiator, but still, a compound with degraded dry etching resistance is used in this literature.
PTL 6 discloses a curable composition for imprinting which contains (meth)acrylate having an aromatic group and a photopolymerization initiator. The composition has excellent dry etching resistance compared to (meth)acrylate of the related art, but it cannot be said that the dry etching resistance is excellent enough.